Now we know. My old smartphone, A Sammy S8, cannot talk to 2 bluetooth audio devices at the same time, I tried it by trying to make it play music to both the BT headphone dongle and to my car audio at the same time. It also cannot manage to send sounds to its headphone socket and the BT dongle at the same time. I guess that I am going to need two long earphone extension cables and a splitter from the dongle to the two radio speaker boxes and then try to lay the cables where nobody might trip over them.
I can feel some soldering about to happen.
Thanks for all of your inputs on this,
Rans6......